Method for removing volatile matter from rolls of sheet material in preparation for coating under vacuum



Aug.

H. BANCROFT 2,518,268

G. THOD FOR REMOVING VOLATILE MATTER FROM ROLLS OF SHEET MATERIAL INPREPARATION FOR COATING UNDER VACUUM Filed Jan. 21, 1948GEOEGEHBA/YC/POFT INVENTOR.

ATTORNEYS Patented Aug. 8, 1950 METHOD FOR REMOVING VOLATILE MAT- TERFROM ROLLS OF SHEET MATERIAL IN PREPARATION FOR -LCOATING UNDER VACUUMGeorge Herbert Bancroft, Rochester, N. Y., assignor, by mesneassignments, to Eastman Kodak Company, Rochester, N. Y., a corporationof New Jersey Application January 21, 1948, Serial No. 3,473

6 Claims. (CI. 3416) This invention relates to a method of preparingrolls of sheet material for coating under vacuum.

It is an object of this invention to provide a method for preparingrolls of sheet material for the application of thin layers of metal orother substances in a vacuum coating apparatus. A further object is toprovide a method of preparing the surface of rolls of sheet material forthe application of an adherent film by means of a vacuum coatingapparatus. A further object is to provide a method for the preparationof long strips of material for the application of an adherent coating bymeans of a vacuum coating apparatus. Another object is to improve thestate of the art. Other objects will appear hereinafter.

These and other objects are accomplished by this invention whichprovides a method ofpreparing the surface of rolls of sheet material,sometimes referred to as strip stockiby re peatedly running saidmaterial from one spool to another in an atmosphere in which thepressure is about 10 microns Hg, and at a rate 'in excess of linear feetper minute.

I have discovered that the gases at the surface of sheet material arealmost instantaneously removed by a vacuum of 10 microns; and furtherthat, when the surface gases are thus removed, the dissolved gases fromthe interior of the sheet slowly diffuse to the surface of'the sheet ata diifusion rate which is not appreciably affected by the presence orabsence of vacuum at the surface during such difiusion. Thus, thedegassing can be carried out at high linear rates of exposure, as forexample at 2 5 to 100 ft. per minute rather than a few inches perminute, since the direct application of vacuum to the surface of thesheet throughout the degassing period is unnecessary. Degassing, inaccordance with this invention, is readily effected at a pressure of 10microns Hg even though the subsequent coating operation is to be carriedout at a pressure of 1 micron.

In the accompanying drawings wherein like numerals refer to like parts,Fig. 1 represents a degassing apparatus of the type in which the stripmaterial is exposed to an atmosphere of very low pressure.

Fig. 2 is another view of the apparatus of Fig. 1.

Referring to FigsQl and 2, degassing chamber 8Ilhas a cover plate 82mounted on wheels 83 for convenience in handling. Wheels 83 move ontrack 84. Cover plate 82 makes gas-tight connection with baseplate 85during operation. Baseplate 85 is held by supporting member 88.

Extending perpendicularly from baseplate 85 is column 86 which rigidlysupports end plate 81. Extending between baseplate 85 and end plate 81are rollers 89 and 9i. Rollers 9| are idlers while rollers 89 arerotated by pulleys 92 which are driven by belts 93 running betweenpulleys 92 and motor 94. Control panel 95 is used to reverse and varythe speed of motor 94. The two shafts rotated by pulleys 92 pass throughgas-tight bearings in baseplate 85.

Conduit 66 is connected to a source (not shown) of high vacuum of theorder of 10 microns Hg. Conduit 56 is a bypass which may be connected toa mechanical pump (not shown) for taking the pressure from atmosphericdown to about 1 mm. Hg.

In operating the device of Figs. 1 and 2, two rolls of sheet material,such as 500-foot rolls of cellulose acetate sheeting, are placed on oneof rollers 89, unrolled around idler rollers 9|, and fastened to theother of rollers 89. The system is evacuated to a pressure of about 10microns Hg. This may be effected by means of an ejector or difi'usionpump working in combination with a, mechanical backing pump at conduits56 and 66. The evacuating system should be of substantial capacity iflow pressure is to be maintained during the period the sheeting materialis giving off substantial quantities of gases. Control panel 95 ismanipulated so that force is applied to pulleys .92 and the speed isadjusted so that upwards of 25 linear feet per minute of material isexposed to the low pressure atmosphere prevailing in the interior of theapparatus.

When all of the material is rolled on roller 89, the controls aremanipulated in order to reverse the rolls and the material is rerolledat a speed This process is repeated until the material ceases to giveoff volatile matter at a rate which would interfere with the subsequentdeposition of coating materials thereon. The number of times thematerial must be exposed varies with the thickness of the material, thecomposition of the material and the rate of exposure. At an exposurerate of feet per minute most of the volatile matter present in thincellulose acetate sheeting is removed in about six exposures and thematerial will be suitable for the application of a coating after about12 exposures. At a rate of 100 feet per minute most of the volatilematter will be removed after about 15 exposures and the material will besuitable for the application of a coating after about exposures. Ratesin excess of 100 feet per minute are feasible and cut down the totaltime necessary in order to place the material in proper condition forthe application of a coating; however, the number of exposures necessaryincreases as the. rate increases.

After the volatile material has been removed from the sheeting the rollsare taken from the vacuum apparatus in tightly rolled form. If thesheeting material is an air-tight plastic, only the outer surface willbe exposed to the atmosphere where it can absorb volatile matter. Theinterior remains free of volatile matter and after storage for a numberof hours at atmospheric pressure it may be exposed to a coating unitwithout any further treatment in the vacuum degassing chamber.

While the invention has been described in considerable detail withreference to a preferred embodiment thereof, it will be understood thatmany modifications and variations therein may be made without departingfrom the spirit and scope of the invention as it is defined by theappended claims.

What I claim is:

1. The method of bringing sheet material into condition suitable forsubsequent application of coating material thereon under vacuum, whichmethod comprises degassing said sheet material to effectively removedissolved gases therefrom by repeatedly and alternately exposingunrolled portions of said sheet material for short periods of time tovacuum effective to remove occluded gases adjacent the surfaces of thesheet and maintaining said portions in a rolled condition forsubstantially longer periods of time suflicient to allow diffusion ofgases from the interior of the sheet to the surfaces thereof, saiddegassing being effected by repeatedly unrolling and rerolling saidsheet material in an atmosphere of about 10 microns Hg pressure at alinear rate of at least 25 feet per minute.

2. The method of conditioning sheet material to effect substantialremoval of dissolved gases therefrom which comprises degassing saidsheet 10 microns Hg, exposing said sheet material to said reducedpressure while winding said material from one spool to another, andrepeating said windin and unwinding at a linear rate of at least 25 feetper minute until occluded gases cease to diffuse to said surfaces insubstantial quantity.

3. The method of conditioning strip stock which comprises removingdissolved gases from Gil 4 said stock by repeatedly and alternatelysubjecting unrolled portions of said stock for short periods of time tovacuum effective to remove occluded gases adjacent the surfaces of saidstock and maintaining said portions in a rolled condition forsubstantially longer periods of time sufllcient to allow diffusion ofgases from the interior of the sheet to the surfacesthereof, saidremoval of gases being effected by subjecting said strip stock in rollform to a pressure of about 10 microns Hg, unwinding said roll andrewinding it at a linear rate in excess of 25 feet per minute, andrepeating the operation of unwinding and rewinding said roll at a linearrate in excess of 25 feet per minute until gases is substantiallyremoved from said strip stock.

4. The method of conditioning sheet material such as cellulose acetatesheeting and the like to remove from said sheet material gases whichwould otherwise be evolved during a subsequent application of coatingmaterial to said sheet material under vacuum of the order of 1 micron ofmercury, which method comprises progressively unrolling andsimultaneously rerolling sheet material in an atmosphere of about 10microns Hg pressure, said unrolling and rerolling being repeated aplurality of times, the total time in which any given portion of saidsheet material is unrolled being substantially less than the total timenecessary for degassing a given portion of said sheet material in asingle sustained exposure, the linear rate of said unrollin andrerolling being at least 25 feet per minute. I

5. The method of conditioning sheet material such as cellulose acetatesheeting and the like to remove from said sheet material gases whichwould be evolved during a subsequent application of coatin material tosaid sheet materia1 under vacuum of the order of 1 micron of mercury,which method comprises progressively unrolling said sheet material at alinear rate of at least about 25 feet per minute while subjecting thesheet material to vacuum of about 10 microns of mercury and therebysubjecting at least 25 feet of unrolled sheetmaterial per minute to saidvacuum of about 10 microns of mercury to remove gases from the surfaceof said unrolled sheet material, and simultaneously rerolling said sheetmaterial at said linear rate of at least 25 feet per minute, andrepeating said simultaneous unrolling and rerolling a plurality oftimes, whereby any given portion of said sheet material is in the rolledcondition substantially longer than said sheet is in the unrolledcondition. I

6. In the application of thin coatings of metal to plastic sheetmaterial by high vacuum evaporation processes, which plastic sheetmaterial normally contains an undesirable amount of dissolved gaseswhich tend to interfere with proper application of metal coatings tosuch sheet material by high vacuum evaporation coating processes, themethod. of preparing such sheet ma.- terial for subsequent coatin byevaporation of coating material under vacuum which comprises removingsubstantially all of said undesirable amount of dissolved gases fromsaid sheet material by rapidly unrolling and simultaneously rerollingsaid sheet material in an atmosphere maintained at a pressure of about10 microns of mercury and thereby exposing progressive portions of saidsheet material to said atmosphere, said exposing of each saidprogressive portion being insuflicient to effect substantially completedegassing of said portion, and repeating said unrolling and rerolling aplurality of times whereby

